The present invention relates broadly to a full duplex communication system, and in particular to a full duplex communication system apparatus using frequency selective limiter units.
In the prior art, conventional filter type duplexers use a combination of bandpass and bandstop filters to direct RF energy from the transmitter to the antenna and from the antenna to the receiver. If either the transmitter or received frequency changes, the duplexer must be retuned in order to maintain efficient operation, which is usually a time consuming and complex process. The stability of the filters and their associated losses are also cause for concern in the filter type duplexer. Full operation duplexers for single antenna systems have been built using circulators but the level of isolation of the receiver from the transmitted power is limited to the degree of matching of the antenna to the system. Wide excursions in transmitted frequency usually result in large reflections from the antenna, thus the circulator duplexer is generally restricted to low power systems. In addition, large reflections may also occur if a highly reflective body is accidentally placed in front of the antenna. When these high power levels reach the receiver, the intermodulation performance suffers, and the receiver front end may also be permanently damaged. The present microwave duplexer apparatus provides the means for a full duplex communication system which overcomes the aforementioned prior art problems.